Sooooo I have a 20g long that was used as my feeder tank for Suzi.... and a few others.

My problem is....

I have cleaned this tank numerous times with WipeOut! (Dimethyl Benzyl Ammonium Chloride)
And glass cleaner once in a while....

My friend bought a Betta fish.... It's in this tiny tank and I find it rather uncomfortable for this fish. I want to donate my 20 gallon to her so that her Betta "Spike" can have a good home with room to grow old and swim around as a fish was intended to do. I can't stand it when people buy a Betta fish and leave it in the container it came in, or think that a small vase is good enough! I feel the same about people who do this with any species of fish....

Is there any way I can make this tank safe to hold water and support fish again?

Thank you in advance !

Jonathan!